1. Field of Invention
The present invention relates to a push-to-talk over cellular (PoC) service, and particularly to a PoC system and a method for distributing media data in PoC.
2. Description of the Related Art
The push-to-talk (PT) method is derived from the walkie-talkie technology and has been broadly used in cellular and Internet environments today. Open Mobil Alliance (OMA) further established a PoC working team for setting the pertinent standards. Quite distinguished from a walkie-talkie system, however, with a PoC system a user must request all online members to be communicated to establish a communication group and to participate in the group prior to obtaining the PTT services. In addition, during establishing the communication group, a voice data delivering path must be decided, and once the communication group is successfully established only a member is allowed to speak while the other members are listening to the speaker in a communication session.
FIG. 1 is a schematic flowchart for conventionally distributing media data in PoC. Referring to FIG. 1, according to the pertinent standards set by OMA, a PoC system associated with a communication group can include a controlling server 110, a first participating server 120 and a second participating server 130, wherein the two participating servers are distributed in different domains, and different clients (members of the group) 142, 144, 146 and 148, which are connected to the corresponding participating server, respectively. During establishing a communication group, the clients 142, 144, 146 and 148, the participating servers 120 and 130 and the controlling server 110 coordinate the voice support capabilities of both parties through SIP signals (session initiation protocol signals) and further decide the manner and paths for delivering media data. Afterwards, the members of the communication group (different clients) deliver voice data packets to each other via the paths.
From FIG. 1 it is clear that the client B 142, the client C 144 and the client D 146 are stationed at a same domain and managed/served by the first participating server 120. The controlling server 110 is in charge of managing/serving the whole communication group, no matter whether the clients as receivers belong to a same participating server or not. Once the voice data sent from the client A 148 is received via the second participating server 130, the controlling server 110 would send a voice data to every member of the communication group except for the sender client A 148. Therefore, according to such a scheme of distributing media data, the same voice data packet would be sent to the first participating server 120 repeatedly for three times; the first participating server 120 resends the same voice data packet respectively to the client B 142, the client C 144 and the client D 146, i.e. a total of three times. In short, using the conventional scheme to distribute a voice data, it needs to send the same voice data to every client, which results in sending the same voice data packet repeatedly for multiple times and accordingly wasting the Internet resource and bandwidth.